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As the need for nano-precision has become
increasingly important in many fields of research and manufacturing – such
as microelectronics fabrication, laser/optical system applications, life
sciences, materials, aerospace and biological research – so has the need
to implement vibration isolation technology for stabilizing academia’s and
industry’s most critical instrumentation to facilitate operation under
extremely precise requirements operating at atomic-scale
resolutions.
The need to eliminate vibration
The need to
provide adequate vibration isolation presents an increasingly important and
complicated challenge, particularly at very low frequencies.
Vibration
influencing high-resolution sub-micron instrumentation can be caused by a
multitude of factors. Within the building itself, the heating and ventilation
system, fans, pumps and elevators are just some of the mechanical devices that
create vibration. How far away sensitive instrumentation is from these
vibration sources, and where in the structure the equipment is located, will
determine how strongly the equipment will be influenced. External to the
building, the equipment can be influenced by vibration from adjacent road
traffic, nearby construction, aircraft, and even wind and other weather
conditions that can cause movement of the structure.
These internal and
external influences cause low-frequency vibration in the 0.5Hz to 50Hz range,
which is transmitted through the structure and into sensitive parts of
instrumentation, compromising resolution, image quality, and the integrity of
data.
Inadequate isolation
Many
vibration isolators, particularly at frequencies below 10Hz, deliver limited
isolation vertically and even less isolation horizontally. In fact, such
isolators create vibration isolation problems in the region of their resonant
frequency. All isolators will amplify at their resonant frequency then start
isolating above this frequency. Pneumatic isolators, for example, will amplify
vibration in a typical range of 1Hz to 4Hz. Sensitive instruments, which are
typically manufactured with internal pneumatic isolation, are, therefore, often
subject to problems with vibration.
Another option in use is active feedback
electronic-force cancellation systems, which incorporate the use of sensors,
actuators, and control algorithms to detect and mitigate vibration.
Active systems have limited dynamic range,
however. They have a tough time dealing with vibration input that is either too
large or too small. Vibrations that are too large can cause the system to go
into positive feedback. Vibrations that are too small may not even be detected.
To achieve a high level of precision in vibration-critical applications,
feedback electronic-force cancellation systems must balance a complexity of
inertial feedback in response to incoming vibrations. This can be challenging
for active systems when the inertial feedback is applied to incoming
low-frequency vibrations horizontally.
As sub-micron research continues to advance
at an accelerated rate, the need to protect sensitive instrumentation –
like electron microscopes, scanning tunneling microscopes, laser
interferometers, and optical profilers – with better vibration isolation
is critical.
Negative-stiffness – the technology
behind sub-micron advanced technology
There is a more advanced
vibration isolation technology in use when it comes to protecting sensitive
sub-micron instrumentation to low-Hertz vibrations. Introduced in the mid-1990s
by
Minus K Technology, Negative-Stiffness vibration
isolation has been widely accepted for vibration-critical
applications, largely because of its ability to effectively isolate lower
frequencies, both vertically and horizontally.
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